Chemistry and Physics. 477 



hermetically sealed, the tops carefully ground and sealed with 

 mercury. The substances employed were themselves carefully 

 purified. The nitrogen thus obtained when examined in a tube 

 furnished with external electrodes, gave a spectrum free from the 

 lines of hydrogen or hydrocarbons. The observation of Thomson 

 and Threlfall in 1887 that nitrogen suffers a diminution of vol- 

 ume on passing the electric discharge through it, the author con- 

 firms. But he finds that this effect is not due to a molecular 

 condensation of the gas as originally supposed; but is owing to 

 the production of a compound between the mercury of the gauge 

 and the nitrogen, probably a nitride of mercury analogous to the 

 trimercuramine of Plantamour. This compound appears as a 

 brown film on the glass when the discharge passes through the 

 nitrogen over mercury at about 8 mru pressure ; nearly the whole 

 of the nitrogen being eventually converted into it. It decom- 

 poses at about 200° and re-forms on cooling. — Phil. 3Iag., V, 

 xxxv, 1, Jan. 1893. G. f. b. 



5. On the Preparation of Carbon under High Pressure. — A 

 series of experiments has been made by Moissact upon the influ- 

 ence of pressure on the crystallization of carbon at high tempera- 

 tures. When carbon is dissolved in iron between 1100° and 

 3000°, either graphite or a mixture of graphite and amorphous 

 carbon separates at the ordinary pressure on cooling. If how- 

 fiver, the cooling be effected under a high pressure the phenomena 

 are quite different. To produce this pressure the mass of iron is 

 heated up to 2000° or 3000° and the exterior is rapidly cooled by 

 means of water; this exterior is thereby solidified and the still 

 liquid interior, expanding as it solidifies produces an enormons 

 pressure. Or, charcoal made from sugar is compressed in a soft 

 iron cylinder closed with a screw plug, and the cylinder is 

 plunged into a crucible containing melted iron. The crucible is 

 withdrawn from the fire and placed in water until its exterior is 

 at a dull red, after which it is cooled in the air. By these 

 processes three forms of carbon are obtained, the proportion of 

 each depending on the conditions of the cooling ; which are (1) 

 graphite, (2) thin contorted, maroon colored flakes, and (3) dia- 

 mond. The diamond is obtained as grains of gray-black car- 

 bonado, of sp. gr. 3*0 to 3 "5 and as transparent fragments, having 

 a waxy luster and marked with striae. Both these varieties leave 

 a minute ash when burned. Silver also has the power of dissolv- 

 ing carbon. If this metal be heated to boiling in a crucible 

 brasqued with charcoal and then rapidly cooled on the outside by 

 plunging it into water, carbonado of sp. gr. from 2-5 to 3 '5 is ob- 

 tained in small plates. — C. R., cxvi, 218, Feb. 1893. g. f. b. 



6. On the Properties of Diamonds. — In a subsequent paper 

 Moissax has given the results of an investigation to determine 

 the temperature at which diamonds begin to burn in oxygen, 

 these temperatures being measured by means of a thermoelectric 

 couple. As the temperature is slowly raised, the combustion 

 takes place slowly and without the production of light, the only 



